Monoalkyl carbonates in carbonated alcoholic beverages Marcelo Rabello Rossi, Denis Tadeu Rajh Vidal, Claudimir Lucio do Lago ⇑ Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, CEP 05508-000, São Paulo, SP, Brazil article info Article history: Received 26 September 2011 Received in revised form 22 November 2011 Accepted 16 January 2012 Available online 24 January 2012 Keywords: Monoethyl carbonate Alcoholic beverage Beer Capillary electrophoresis Conductivity detection abstract The presence of monoethyl carbonate (MEC) in beer and sparkling wine is demonstrated for the first time, as well as the formation of this species in drinks prepared with a distilled beverage and a carbonated soft drink. A capillary electrophoresis (CE) equipment with two capacitively coupled contactless conductivity detector (C 4 D) was used to identify and quantify this species. The concentrations of MEC in samples of lager beer and rum and cola drink were, respectively, 1.2 and 4.1 mmol/l, which agree with the levels of ethanol and CO 2 available in these products. Previous results about the kinetics of the reaction suggest that only a small amount of MEC should be formed after the ingredients of a drink are mixed. However, in all three cases (whisky and club soda; rum with cola; gin and tonic water), MEC was quickly formed, which was attributed to the low pH of the drinks. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction A monoalkyl carbonate (MAC) can be thought of as a salt de- rived from an alkyl carbonic acid (ACA), which is the half-ester of an alcohol and carbonic acid. Independently of the nomencla- ture and a formal origin, studies about synthesis and properties of such species are mainly conducted in harsh conditions, involv- ing at least low temperature, high pressure, or anhydrous med- ium. For example, methylcarbonic acid melts at 36 °C followed by decomposition into methanol and carbon dioxide (Gattow & Behrendt, 1972). Their salts are stable at room tem- perature, but decompose in water (Gattow & Behrendt, 1972; Miller & Case, 1935; Pocker, Davison, & Deits, 1978). Despite this reactivity, the equilibrium constants obtained during studies about hydrolysis suggest that MACs can be formed in aqueous medium from carbonate/bicarbonate and an alcohol (Sauers, Jen- cks, & Groh, 1975). In fact, monoethyl carbonate (MEC) could be observed by 13 C NMR in aqueous/ethanolic medium in a study about the mechanism of bicarbonate activation of hydrogen per- oxide (Richardson, Yao, Frank, & Bennett, 2000). In a recent study, we demonstrated the formation of these species in mainly aqueous media by using capillary electrophoresis (CE) with a capacitively coupled contactless conductivity detector (C 4 D) (Vi- dal, Nogueira, Saito, & do Lago, 2011). Ionic mobilities, diffusion coefficients, and hydrodynamic radii of 11 alcohols were deter- mined using this technique. Scheme 1 shows the set of reactions involved in the formation and decomposition of a MAC in aqueous medium. The reactions are sketched as equilibrium, because all steps are reversible, although the kinetics are not fast for all of them. One can note that the lower the pH, the higher the CO 2 production, and thus the low- er the concentrations of the aqueous (HCO  3 and CO 2 3 ) and alco- holic (MAC) anionic forms. On the other hand, a high pH favours CO 2 3 . Thus, there is a pH range within which a MAC can be main- tained in appreciable amounts. In the previous study, MACs were detected by capillary electrophoresis from pH 4.5 up to 10.5. Among the MACs, some are of special interest in biochemistry and food chemistry, such as MEC. The equilibrium constant, de- fined by Eq. (1), is (2.11 ± 0.09) at 20 °C(Vidal et al., 2011), suggests that MEC is the primary form of carbonate in concentrated etha- nolic media. Of course, for a low level of alcohol and/or carbonate in water, MEC is not a major constituent, but it should be consid- ered. For example, based on the equilibrium constant, one can anticipate that beer should contain monoethyl carbonate at a level as high as 2.3 mM, considering a concentration of 6% (v/v) of etha- nol and 2.5 g/l of total carbonate. K eq ¼ ½CH 3 CH 2 OCO  2 ½H 2 O ½CH 3 CH 2 OH½HCO  3  ð1Þ The present work aims to prove the existence of MEC in some alcoholic beverages and demonstrate that it can be formed or decomposed depending on the way the beverage is prepared be- fore drinking. 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2012.01.039 ⇑ Corresponding author. Tel.: +55 11 3091 3828; fax: +55 11 3091 3781. E-mail addresses: rabello@usp.br (M.R. Rossi), denistadeu@gmail.com (D.T.R. Vidal), claudemi@iq.usp.br (C.L. do Lago). Food Chemistry 133 (2012) 352–357 Contents lists available at SciVerse ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem